Telegraphone and like apparatus



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TELEGRAPHONE AND LIKE APPARATUS Filed Feb. 9. 1940 ..J Anlauf/5e FIGQ.

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Patented ug. 5,V 1941 UNITED f 'rELEGRAPnoNeANp ama APPARATUS Joseph Star, New' York, N. Y., assignorto Radio Development and'Reaearch Corporation, New York. N. Y., a corporation Application Februaryg, v1940, SerialNo. 318154 v 2 claimt?. (Ci. 179-,1002) This invention pertainsto telegraphone lreproducingsystems and more particularly to a twon Way telegraphoneI reproducing system.

, the frequency response of one head was substantially identical with that of the other head. If

multi-channel reproducing system to effect reproduction of separate bands of high frequency and low frequency magneticimpulses as recorded on a magnetizable tape. -This is accomplished by employing two or Amore reproducing coils or pick-up heads, each responsive to a separate band of frequencies, and each head having a predetermined responsive characteristic. of the separate head are connected to separate The outputs' The present invention contemplates utilizing a amplierswith the output of the amplifiers con- The arrangement also contemplates the output of the separate pick-up heads going to a mixer. It is understood that the output of the mixer in each case will ulti- .matelylead to a reproducing device, such as a loud speaker. 4 .l l,

J It is therefore an object of vthis invention to provide a telegraphone reproducing system employing a plurality of pick-up heads, one pick-up head having a predetermined response characterlstic different from another pick-up'head, in order to obtain substantially uniform response to a wide range of frequencies.

A further object of the invention is to provide a telegraphone reproducing system having a 'wide range of' substantially uniform frequency vby means of a plurality of pick-up heads, each -pickup head being connectedeither directly, or in,- directly to a mixer which permits adjustment of the relative amount of output derived from each of the several pick-up heads.

A further object is the provision of a repro- .ducing system of the class described having a more convenient method bf equalization, obviating the necessity for using coils and condensers,

or extensive equalizers asis conventional in the single channel systems.

A further object is to provideatelegraphone reproducing system employingtwo pikfup heads, one head being responsive tothe upper portion of the total frequency range, and thelother'head being responsive to the lower 4portionof the total frequency range the output ,of each head` going to a separate amplifier, the output of each am plifier being connected to Aa common mixer, and each of the amplifiers having an independent gain control to permit adjustment of the signal intensity from its respective pick-up head.

Further and other objects will become apparent to those skilled in the art from a pursual of the following specification;

' Fig. 1 is a schematic wiring diagram of a ccnventional amplifier with a gain control.

Fig. 2 is a schematic wiring diagram of a con ventionalvmulti-ehannel mixer Iwith gain controls.

Fig. 3 shows a plurality of pick-up heads connected through individual amplifiers to a mixer.

Fig. 4 shows two pick-up heads connected directly to a mixer.

Fig. 5 shows a graphical representation of the intended frequency response characteristic of the reproducingsystem. l

Referring to the drawing, and particularly Fig. 3 the magnetizable tape t, may be any suitable kmagnetic material. Pick-up heads and t, have pole pieces il, and it, respectively, which pole pieces engagev the tape il, for the purpose of reproducing the signals magnetically impressed thereon.- The pole pieces `of the pick-up heads are staggered in the present showing, but they may be directly` opposite each other depending upon magnetization used'for recording. In the manner shown the pole pieces will each supply a convenient magnetic path for the changing flux resulting from the passage of the magnetized tape, and cause this ,flux to pass through the center of its associated coil. This changing flux generates a voltage in the coil. The pick-up I heads i and 8 have difieren-t frequency response characteristics brought about by suitableV design. .The factors affecting these characteristics are coil inductance and resistance, `core material and dimensions, etc. By suitable design the head is made responsive tothe desired channel, or band of frequencies. The low frequency head, for exlample, is shown as having been designed for response to a range of frequencies fromsay 2u vertical axis representing output in decibels, and the horizontal axis representing a substantially logarithmic scale of frequencies. Frequency response characteristics are shown plotted with respect to these axes. 'I'he range of relative output energy has been arbitrarily selected from zero to 40 decibels, and the range of frequencies has been indicated as extending from 1 to 8000 cycles per second. These are ranges commonly encountered in commercial equipment.

The two solid curves represent the frequency response characteristics of the low and high frequency channels, adjusted bythe volume controls to give substantially uniform response over the entire range. 'I'he dotted curves indicate the effect of changing the volume controls. If, for example, the individual volume control 21 associated with the high frequency 'channel were adjusted to increase the channel output, the right hand characteristic curve would be shifted to one of the upper dotted positions, the amount of eachshift being determined by the magnitude` of the change involume adjustment. Adjustment of the common volume control 39 will shift both characteristics simultaneously without altering their relative positions with respect to each other. 'I'he shape overall response characteristic will4 therefore depend upon the adjustments of the individual channel controls, 26 and 21 with respect to each other. Predominance may be given, if desired, to eitherchannel by independently increasing its respective volume, or gain although ordinarily the most faithful reproduction will be obtained when the characteristics occupy the relative positions indicated by the solid curves in Fig. 5.

The output of the head 1. is connected to the input terminals I4 and I5 of the amplifier II.

The output terminals I6 and I1 are connected by wires I8 and I9 respectively to the input terminals 20 and 2I of the mixer 22. The output of the mixer has terminals 23 and 24 which connect to a loud speaker or other load. Since the amplifiers II and I2 are substantially the same as a conventional amplifier 25', then the gain control I3 could vary the signal intensity of the output of the individual heads before the signals were communicated to the input of the mixer. The pick-up head 8 is connected to the input terminals 33 and 34 of the amplifier I2. The output terminals 35 and 35 of the amplifier I2, are

connected by conductors 39 and 40, respectively v to the terminals 36 and 38 respective of the mixer.

It is to be understood that the expression mixer includes any suitable device for combining two or more signals, for the purpose of bringing the signals to a common output.

'I'he gain controls 26 and 21 of the mixer 32, Fig. 2, would be particularly adapted for use when theA pick-up heads 1 and 8 were connected directly to the inputterminals 20, 2|, 31, 38 of the mixer shown in Fig. 4. l

The present system may also be used where it is desirable to use av separate speaker or load connected to each pick-up head, vand have the minals 42 and 43, while a second speaker may be connected across terminals 46 and 41. The

' result of the two speakers having their audible signals mixed would permit the use of the high and low frequency heads used in conjunction a. single magnetizable recording tape. The mixer is used where singe sound reproducer, or speaker is used.

From the foregoing it will be seen that by using two pick-up heads having different frequency response characteristics, the reproducing system will effectally accentuate either the high or low frequency channel, as desired, will combine them so that the acoustic output of the speaker or speakers will produce the desired tonal effect.

It is furthenpointed out, by comparing Figs. 3 and 4, that the essence of the invention resides in utilizing a plurality of pick-up heads each having a separate predetermined response characteristic'. 'I'he primary advantage of the invention results from overcoming the great practical difficulty of designing and constructing a single pick-up head to respond uniformly to wide range of frequencies. Those design factors which improve response to high frequencies are detrimental to sensitivity in the low frequency range, and vice versa. By splitting the desired range of frequencies into two or more bands, and providing a specially designed pick-up head for each band, the problem of design and commercial manufacture is greatly simplified. l

While specific details of the invention have.

been herein shown and described, the invention is not confined thereto, as changes and alterations may be and may become apparent to those skilled in the art Without departing from the spirit thereof 'as delned by the appended claims.

Having thus described the invention, what I claim as new and desire to secure-by Letters Patent of the United States. is:

1.'A telegraphone reproducing system of the class described having two pick-up heads one being disposed on either side ofa movable magnetizable material, a magnetic core securely afxed within each of the pick-up hea'ds, saidcore adaptedfto protrude from the coil of each of said heads to engage the magnetizable material, one of said pick-upheads having a predetermined response characteristic adapted to be responsive to a given band ofl frequencies, the other of said pick-up heads having a response characteristic adapted to be responsive to a band of frequencies different from said first pick-up head. the output of each of said pick-up heads going into the input of the mixing device, andA a sound reproducing device connected to the output of the mixing device.

2. A telegraphone reproducing system employing two pick-up heads each of said pick-up heads comprising a coil and a core securely amxed therein, one of said pick-up heads being responsive to the upper portion of the total frequency range and the other head being responsive to the lower portion of the total frequency range of the magnetic frequencies` impressed upon the movable magnetizable material, the output of said input heads connected. to'the input of the mixingv device, and a reproducing device connected to the output of the mixing device.

. JOSEPH STAR. 

